Attenuator system for microwave-assisted chemical synthesis

ABSTRACT

An instrument for microwave-assisted chemical processes is disclosed that provides greater flexibility in carrying out microwave-assisted chemistry under varying conditions. The instrument includes a source of microwave radiation, and a cavity in communication with the source, with the cavity including at least one wall formed of two engaged portions that form a barrier to the transmission of microwaves when so engaged. The engaged portions are disengagable from one another, and one of the portions includes a microwave-attenuating opening.

FIELD OF THE INVENTION

[0001] The present invention relates to microwave-assisted chemistry,and in particular relates to a microwave instrument that offersparticular advantages useful for chemical synthesis reactions.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to devices and methods formicrowave-assisted chemistry. As generally recognized in the chemicalarts, many chemical reactions can be initiated or accelerated byincreasing the temperature—i.e. heating—the reactants. Accordingly,carrying out chemical reactions at elevated (i.e., above ambient)temperatures is a normal part of many chemical processes.

[0003] For many types of chemical compositions, microwave energyprovides an advantageous method of heating the composition. As is wellrecognized in the art, microwaves are generally categorized as havingfrequencies within the electromagnetic spectrum of between about 1gigahertz and 1 terahertz, and corresponding wavelengths of betweenabout 1 millimeter and 1 meter. Microwaves tend to react well with polarmolecules and cause them to rotate. This in turn tends to heat thematerial under the influence of the microwaves. In many circumstances,microwave heating is quite advantageous because microwave radiationtends to interact immediately with substances that aremicrowave-responsive, thus raising the temperature very quickly. Otherheating methods, including conduction or convection heating, areadvantageous in certain circumstances, but generally require longer leadtimes to heat any given material.

[0004] In a similar manner, the cessation of application of microwavescauses an immediate corresponding cessation of the molecular movementthat they cause. Thus, using microwave radiation to heat chemicals andcompositions can offer significant advantages for initiating,controlling, and accelerating certain chemical and physical processes.

[0005] In recent years, much interest in the fields of chemicalsynthesis and analysis has focused upon the use, synthesis or analysisof relatively small samples. For example, in those techniques that aregenerally referred to as “combinatorial” chemistry, large numbers ofsmall samples are handled (e.g., synthesized, reacted, analyzed, etc.)concurrently for the purpose of gathering large amounts of informationabout related compounds and compositions. Those compounds orcompositions meeting certain threshold criteria can then be studied inmore detail using more conventional techniques.

[0006] Handling small samples, however, tends to present difficulties inconventional microwave-assisted instruments. In particular, small massesof material are generally harder to successfully affect with microwavesthan are larger masses. As known to those of ordinary skill in this art,the interaction of microwaves with responsive materials is referred toas “coupling.” Thus, stated differently, coupling is more difficult withsmaller samples than with larger samples.

[0007] Furthermore, because of the nature of microwaves, specificallyincluding their particular wavelengths and frequencies, theirinteraction with particular samples depends upon the cavity into whichthey are transmitted, as well as the size and type of the sample beingheated.

[0008] Accordingly, in order to moderate or eliminate coupling problems,conventional microwave techniques tend to incorporate a given cavitysize, a given frequency, and similarly sized samples. Such techniquesare useful in many circumstances and have achieved wide acceptance anduse. Nevertheless, in other circumstances when one of theseparameters—sample size, material, microwave frequency—is desirably ornecessarily changed, the cavity typically has to be re-tuned in order toprovide the appropriate coupling with the differing loads. Statedsomewhat differently, and by way of illustration rather than limitation,in a conventional device a one gram load would require tuning differentfrom a ten gram load, and both of which would require different tuningfrom a hundred gram load, and all of which would differ if the microwavefrequency or type of material is changed.

[0009] As another issue, differently-sized samples are generally mostconveniently handled in reaction vessels that are proportionally sizedbased on the size of the sample. Many instruments for microwave-assistedchemistry, however, are—for logical reasons in most cases—made to handlevessels of a single size; e.g. instruments such as described in U.S.Pat. No. 5,320,804 or open vessels as described in U.S. Pat. No.5,796,080. Thus although such instruments are valuable for certainpurposes, the are generally less convenient, and in some cases quiteineffective for samples, vessels, and reaction other than a certain size(volume) or type.

[0010] As yet another issue, many reactions proceed more favorably underincreased (i.e. above atmospheric) pressure. Controlling and usingincreased pressures for small samples in microwave-assisted chemistrycan, for the reasons stated above and others, be somewhat difficult.

[0011] Accordingly, the need exists for new and improved instruments formicrowave assisted chemistry that can handle small samples, canconveniently handle a variety of sample sizes and vessel sizes and thatcan incorporate and handle higher pressure reactions when desired ornecessary.

OBJECT AND SUMMARY OF THE INVENTION

[0012] Therefore, it is an object of the invention to provide amicrowave instrument suitable for chemical synthesis and relatedreaction and that can handle small samples, can conveniently handle avariety of sample sizes and vessel sizes and that can incorporate andhandle higher pressure reactions when desired or necessary.

[0013] The invention meets this object with an instrument formicrowave-assisted chemical processes that avoids tuning discrepanciesthat otherwise result based upon the materials being heated. Theinstrument comprises a source of microwave radiation a waveguide incommunication with the source, with at least a portion of the waveguideforming a cylindrical arc, a cylindrical cavity immediately surroundedby the cylindrical arc portions of the waveguide, and at least 3 slottedopenings in the circumference of the circular waveguide that providemicrowave communication between the waveguide and the cavity.

[0014] In another aspect the invention is a method of conducting organicsynthesis reactions comprising applying microwave radiation to a sampleusing a frequency to which the sample (solvent, etc) will thermallyrespond, and optimizing the coupling between the applied microwaves andthe (load) sample without adjusting the physical dimensions of thecavity, without physical movement of the cavity (i.e. no tuning screws),without physical movement of the position of the sample and withoutadjusting the frequency of the applied microwaves as the sample heatsand as the reaction proceeds.

[0015] In another aspect, the invention is a pressure-measuring vesselsystem for microwave assisted chemical processes. In this aspect, theinvention comprises a pressure resistant vessel (i.e., it resists theexpected pressure to which it is expected to be exposed) that isotherwise transparent to microwave radiation, a pressure-resistantclosure for the mouth of the vessel, with portions of the closureincluding a pressure resistant synthetic membrane, a pressure transducerexternal to the vessel, and a tube extending from the transducer,through the membrane and into the vessel for permitting the pressureinside the vessel to be applied against the transducer while the closureand membrane otherwise maintain the pressure resistant characteristicsof the vessel.

[0016] In another aspect, the invention is an instrument formicrowave-assisted chemical processes that provides greater flexibilityin carrying out microwave-assisted chemistry under varying conditions.In this aspect, the instrument comprises a source of microwaveradiation, a cavity in communication with the source, with the cavityincluding at least one wall formed of two engaged portions that form abarrier to the transmission of microwaves when so engaged, with theengaged portions being disengagable from one another; and with one ofthe portions further including a microwave-attenuating opening forreceiving a reaction vessel therethrough and into the cavity when theportions are engaged.

[0017] In yet another aspect, the invention is a method of increasingthe efficiency of microwave-assisted chemical reactions. The methodcomprises carrying out a first chemical reaction in a reaction vessel inan attenuated cavity of a microwave instrument, removing the reactionvessel and the attenuator from the instrument, placing a differentreaction vessel and a differently-sized attenuator in the same cavity ofthe instrument, and carrying out a second chemical reaction in thedifferent vessel in the cavity of the instrument.

[0018] The foregoing and other objects and advantages of the inventionand the manner in which the same are accomplished will become clearerbased on the followed detailed description taken in conjunction with theaccompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a front perspective view of an instrument according tothe present invention;

[0020]FIG. 2 is a rear perspective view of the instrument illustrated inFIG. 1;

[0021]FIG. 3 is a partially exploded interior view of the instrumentillustrated in FIGS. 1 and 2;

[0022]FIG. 4 is a perspective view of a cavity and wave-guide accordingto the present invention;

[0023]FIG. 5 is an interior view of the waveguide and cavity illustratedin FIG. 4.

[0024]FIG. 6 is a perspective exterior view of the wage guide, cavityand magnetron of the present invention;

[0025]FIG. 7 is a perspective view of the pressure-measuring assemblyaccording to the present invention;

[0026]FIG. 8 is another perspective view of the pressure-measuringassembly;

[0027]FIG. 9 is a detailed exploded view of the pressure measuringassembly;

[0028]FIG. 10 is an exploded view of the cavity assembly of aninstrument according to the present invention;

[0029]FIG. 11 is a cross-sectional view of a reaction vessel,pressure-measuring means and collet assembly of an instrument accordingto the present invention;

[0030]FIG. 12 is a cross sectional view of the cavity portion of theinstrument according to the invention and including an exemplaryreaction vessel; and

[0031]FIG. 13 is a cross-sectional view almost identical to FIG. 12, butillustrating the features of the invention in relation to adifferently-sized reaction vessel.

DETAILED DESCRIPTION

[0032] An embodiment of the present invention is illustrated inperspective view in FIG. 1 with the instrument broadly designated at 20.Most of the other details of the invention will be shown in otherdrawings, but FIG. 1 illustrates that the instrument 20 includes ahousing 21, a control panel 22, and a display 23. As will be discussedlater herein, the control panel 22 can be used to provide the instrumentwith a variety of information that may relate to the chemical processesbeing carried out, or to set or define certain parameters, such asmaximum pressure or temperature during the application of microwaveenergy to a particular reaction. The control panel 22 can be formed ofany type of appropriate input devices, with buttons 24 beingillustrated. It will be understood, however, that other types of inputdevices, including touch screens, keyboards, a computer “mouse” or otherinput connections from computers or personal digital assistants can alsobe used in any appropriate fashion known to those of skill in this artthat does not otherwise interfere with the operation of the instrument.Similarly, the display 23 is most commonly formed of a controlled oraddressable set of liquid crystal displays (LCDs) but can also comprisea cathode ray tube (CRT), light emitting diodes (LEDs), or any otherappropriate display medium.

[0033] The housing 21 includes a removable upper portion 25, attached byappropriate fasteners 26 (screws or Allen nuts are exemplary) to a lowerhousing portion 27 and a pedestal portion 30, which in turn aresupported by the pedestal feet 31.

[0034]FIG. 1 also illustrates that the housing 21 includes an opening32, which provides access to the microwave cavity in a manner that willbe described with respect to other drawings. As FIG. 1 illustrates, theopening 32 provides much easier access for placing samples into thecavity than in many other types of microwave instruments.

[0035]FIG. 1 also illustrates the sample holder and microwave attenuatorassembly 33, and a collet assembly 91 which will likewise be describedin more detail with respect to other of the drawings.

[0036]FIG. 2 is a rear perspective view of an instrument according tothe present invention that illustrates some additional items. As in FIG.1, FIG. 2 illustrates the upper housing portion 25, the lower housingportion 27, the fasteners 26, the pedestal portion 30, the feet 31, thesample holder and attenuator assembly 33 and the opening 32 in thehousing 25 that provides access to the cavity.

[0037] Additionally, FIG. 2 illustrates that the device includes atleast one cooling fan 34 with a second being shown at 35. The fans 34and 35 serve to cool the electronics and the magnetron portions of thedevice, as well as helping to keep the cavity from becoming overheatedin the presence of ongoing chemical reactions. Other than having thecapacity to appropriately cool the instrument and the cavity, the natureor selection of the fans can be left to the individual discretion ofthose with skill in this art.

[0038]FIG. 2 also shows the power switch 36 and the power cord inlet 37.In order to take advantage of the full capacity of the instrument, inpreferred embodiments, the instrument includes the parallel port 41 andthe serial port 40 for receiving input from or providing output to otherelectronic devices, particularly microprocessor based devices, such aspersonal computers, personal digital assistants or other appropriatedevices. Similarly, FIG. 2 illustrates a connector 42 for the pressuretransducer to be described later herein.

[0039]FIG. 3 is a partially exploded view of the interior of aninstrument 20 according to the present invention. In common with FIGS. 1and 2, the lower portion 27 of the housing and the pedestal portion 30of the housing are both illustrated along with the pedestal feet 31.FIG. 3 also illustrates several of the fasteners 26, as well as the fan34 along with its housing 42.

[0040]FIG. 3 shows the display 23 in exploded fashion along with a firstelectronics board 43 and a second electronics board 44. Basically, theelectronics carried by the boards 43 and 44 are generally wellunderstood in their nature and operation. With respect to the instrumentof the present device, the electronics first control the power from agiven source, usually a wall outlet carrying standard current. Theelectronics also control the operation of the device in terms of turningthe magnetron on or off, and in processing information received from theongoing chemical reaction, in particular temperature and pressure. Inturn, the appropriate processor is used to control the application ofmicrowaves, including starting them, stopping them, or moderating them,in response to the pressure and temperature information received fromthe sensors described later herein. The use of processors and relatedelectronic circuits to control instruments based on selected measuredparameters (e.g. temperature and pressure) is generally well understoodin this and related arts. Exemplary (but not limiting) discussionsinclude Dorf, The Electrical Engineering Handbook, Second Ed. (1997) CRCPress LLC.

[0041] In the embodiment illustrated in FIG. 3, the outer housing of thecavity is visible at 45, along with the housing portions of themicrowave source, illustrated as the magnetron 46. FIG. 3 alsoillustrates the sample holder and attenuator assembly 33, and a motor 47for stirring reactants in a manner described later herein. FIG. 3 alsoillustrates the housing 50 for the second fan 35 present in theillustrated embodiment. Because the sample vessel (not shown) and thesample holder and attenuator assembly 33 are generally quite differentin size than the cavity itself, FIG. 3 illustrates that the attenuator33 according to the present invention further includes an upper rim 51into which lower portions of the sample holder and attenuator assembly33 can rest in a changeable receiving fashion. The features, advantagesand details of the attenuator 33 are discussed in more detail withrespect to FIGS. 11, 12, and 13. The attenuator 33 is in turn held inplace by a pair of retaining rings 52 and 53 into which the attenuator33 is received and which is also held in place by the interlock assemblybroadly designated at 54.

[0042]FIGS. 4 and 5 illustrate aspects of the waveguide and cavityportions of the instrument according to the present invention. In theseillustrations, the waveguide is broadly designated at 55, and includesboth a parallelpiped rectangular portion 56, and a cylindrical portion57 that in preferred embodiments has a rectangular cross section. In theillustrated embodiment, the waveguide 55 is supported on a series oflegs 60 which serve to position the cavity 61 and waveguide 55 incommunication with the magnetron 46 and the other elements within theparticular housing 21. One of the legs, designated at 96, has a slightlydifferent structure to support the motor 47 (not shown). It will beunderstood, of course, that such features as the leg 60 which merelypositions the waveguide within a particular embodiment are not limitingof the present invention. In preferred embodiments the rectangular orparallelpiped portion 56 of the waveguide joins the cylindrical portion57 perpendicularly to a tangent defined by the circumference of thecylindrical waveguide portion 57.

[0043]FIGS. 4 and 5 also illustrate the cavity as broadly designated at61. In particular, the cavity is formed by an inner cylindrical wall 62that forms a concentric cylinder inwardly of the cylindrical cavityhousing 45. An upper waveguide plate 63 and a lower waveguide plate 64define the limits of the waveguide 55 in both its rectangular portion 56and its cylindrical portion 57. The waveguide 55 is constructed of amaterial that reflects microwaves inwardly and prevents them fromescaping in any undesired manner. Typically, such material is anappropriate metal which, other than its function for confiningmicrowaves, can be selected on the basis of its cost, strength,formability, corrosion resistance, or any other desired or appropriatecriteria. In preferred embodiments of the invention, the metal portionsof the waveguide and cavity are formed of stainless steel.

[0044] The top plate 63 (as well as the bottom plate 64) is also held inplace by a series of connectors 65 which can be rivets, screws or nuts,provided that their size and shape avoids undesired interference withthe microwaves in the cylindrical or other portions of the waveguide 55.

[0045] Perhaps most importantly, FIG. 4 illustrates that a plurality ofslotted openings 66 are present in the inner cavity wall 62 forfacilitating the transmission of microwaves from the waveguide 55 intothe cavity 61. It will be understood that because the inner wall 62defines the border of the waveguide 55 and the cavity 61, the slottedopenings 66 can also be described as being in the inner circumference ofthe cylindrical portion 57 of the waveguide.

[0046] In particular, it has been discovered in accordance with thepresent invention that a plurality of such slots in a circularorientation in a static structure in the cavity 61 provides anappropriate amount of coupling with a wide variety of sample sizes ortypes that may be present in the cavity. Although the inventors do notwish to be bound by any particular theory, it appears that the pluralityof slots 66, permit a variety of microwave patterns (modes) to beestablished in the cavity 61, depending upon the load to which themicrowaves are coupled. The cavity includes at least three slots,preferably at least five, and in the presently most preferred embodimentincludes seven slots spaced at least about 40 degrees from each other.Preferably, the slots 66 are oriented parallel to the axis of the cavity61.

[0047] As other details, FIG. 4 illustrates a connector plate 67 andconnecting pins 70 are at one end of the waveguide 55 for connecting thewaveguide 55 to the magnetron 46 or other microwave source, which can,depending upon choice and circumstances, also comprise klystron, a solidstate device, or any other appropriate device that produces the desiredor necessary frequencies of electromagnetic radiation within themicrowave range. FIG. 4 also shows a gas inlet fitting 58 that is partof a system for cooling the cavity that is discussed in more detail withrespect to FIGS. 10, 12 and 13.

[0048] As some additional details, in the preferred embodiments, thecylindrical waveguide completes an arc of more than 180°, and preferablybetween 270° and 360°, and the cylindrical cavity 61 completes a full360°.

[0049]FIG. 5 shows the same details as FIG. 4, but in a broken lineinterior view. Accordingly, FIG. 5 likewise illustrates the overallstructure of the waveguide 55, its rectangular and cylindrical portions56 and 57 respectively, the cavity 61, the slots 66 in the inner wall62, and the supporting legs 60. FIG. 5 also illustrates that thefasteners 65 have a relatively low profile within the waveguide 55 toavoid interfering with microwave propagation therethrough.

[0050] In particular detail, FIG. 5 shows that the waveguide 55 isconnected to the magnetron 46 (not shown) through the launching opening71 in the plate 67. The microwaves can then propagate through therectangular portion of the waveguide 56 into the circular portion 57 ofthe waveguide 55. The structure also includes two walls 72 and 73 thatare positioned in the cylindrical portion 57 of the waveguide justadjacent one of the places where it intersects with the rectangularportion 56. Accordingly, to the extent that standing waves or modes arein the waveguide 55 and cavity 61, they will be confined to theillustrated geometry by the reflecting wall 73. In the absence of thewalls 72 or 73, the modes in the waveguide and the cavity 61 would bequite different because they would interact through a full 360° of thewaveguide housing rather than in the somewhat lesser portion than theydo in the illustrated embodiment.

[0051]FIG. 5 also shows that in the preferred embodiment of the presentinvention there are seven slots 66 in the inner cavity wall 62, witheach of the slots being at least about 40 degrees apart from each of thenext adjacent slots. Furthermore, none of the slots 66 are directly atthe end of the rectangular portion 56 of the waveguide 55 so that themodes that set themselves up in the waveguide 55 and cavity 61 mustenter the cavity 61 after having entered at least a portion of thecylindrical portion 57 of the waveguide 55.

[0052]FIG. 5 also illustrates that in preferred embodiments, the cavityfloor 74 includes a plurality of small openings 75 for ventilation andfluid drainage purposes, with ventilation being expected and liquiddrainage being less frequent, typically in the case of spills. FIG. 5also illustrates a circular shaft 76 that depends from the floor 74 ofthe cavity 61 for permitting optical access to the cavity in a mannerthat will be described later herein.

[0053] Alternatively, FIG. 5 also illustrates the optional use of acavity liner 59 for containing spills, splashes or other incidents inthe cavity 61. The cavity liner 59 optionally includes a small opening68 to facilitate optical temperature measurement through the opening 76in the cavity floor 74 and the window 69. If the cavity liner 59 isformed of a material that is transparent to the optical measurement(typically IR-transparent for IR temperature measurements), the window69 may be unnecessary. The liner 59 is preferably formed of achemically-resistant polymer, and can (depending on the user's cost andbenefits) provide a disposable alternative to physically cleaningreagents or by-products from the cavity 61.

[0054]FIG. 5 also illustrates the dielectric insert 95 that is describedin more detail with respect to FIG. 10.

[0055]FIG. 6 is a complementary view of a number of the elements of theinvention and illustrates the cavity 61 from the perspective of itshousing 45 in conjunction with the rectangular portion 56 of thewaveguide 55 and the magnetron 46. In particular, FIG. 6 offers a largerview of the retaining rings 52 and 53 along with the removableattenuator 33. The attenuator 33 includes an axial opening that will bedescribed in more detail with respect to FIGS. 12 and 13. As describedwith respect to FIG. 3, the retaining rings and the attenuator 33 areheld in place by the interlock assemblies 54. One of the particularadvantages of the invention is that with the use of the retaining rings52 and 53, along with the interlock assembly 54 to retain the attenuator33 in place, the interlock assembly 54 can be relatively easilyreleased, and the attenuator 33 replaced with one that contains adifferent sized opening that in turn supports a different size reactionvessel while still preventing microwaves from propagating past theattenuator 33.

[0056] Thus, the retaining rings 52 and 53, along with the engagedattenuator 33 form the upper horizontal wall of the cavity and a barrierto the transmission of microwaves when so engaged. The retaining rings52 and 53 are fixed to the cavity (i.e., removable only by disassemblingthe instrument with tools), while the attenuator 33 is easily removablefrom the rings 52 and 53 with a simple turning and lifting movement. Theremovable attenuator 33 includes the microwave attenuating opening 118(FIGS. 12 and 13) for receiving a reaction vessel therethrough, and intothe cavity 61. It will thus be understood that in preferred embodiments,the instrument comprises two or more of the removable and engagableattenuators 33 that have differently-sized (from one another)microwave-attenuating openings for receiving differently-sized reactionvessels.

[0057]FIGS. 7, 8, and 9 illustrate detailed aspects of the pressuremeasuring means of the instrument including the transducer assembly 38.FIG. 7 shows the assembly 38 in assembled fashion with a series ofretaining screws 82, a collet adjustment slot 83, and a collet tensionscrew 84 all of which are perhaps best understood with respect to FIG.9.

[0058]FIG. 8 shows the backshell of the assembly 38, apart from thecollet housing 86 which includes the retaining screws 82 that are alsoillustrated in FIG. 7. A pressure transducer 116 is positioned inside atransducer holder 123 which in turn is surrounded by the adjustablecollet assembly 91, the details of which are best illustrated in FIG. 9.

[0059]FIG. 9 is an exploded view of the transducer assembly 38. As inFIGS. 7 and 8, the collet backshell is illustrated at 85, and the collethousing at 86. The setscrews 82 illustrated in FIGS. 7 and 8 are alsoillustrated in FIG. 9.

[0060]FIG. 9 is perhaps best understood with respect to its relation toa vessel (not shown in FIG. 9) that is in the cavity 61 undergoing amicrowave-assisted chemical reaction. Such a vessel, and its cap, areschematically illustrated in somewhat more detail in FIG. 11, but forthe purposes of FIG. 9, it will be understood that a vessel would bepositioned under and in engagement with a vessel receptor 106 that isillustrated in FIG. 9. In order to engage the entire transducer assembly38, and in turn the pressure measuring transducer, with a vessel, thetransducer assembly 38 forms an adjustable device that can move inlinear relationship to its own housing 86, and with respect to a vesselin the cavity. Accordingly, and in order to accomplish this, FIG. 9shows that the transducer assembly 38 includes a plurality (four arepreferred) of collet leaves 107. The leaves 107 are held in flexiblerelationship to the collet trunk 110 by the garter spring 111. Amongother features, the collet trunk 110 includes a plurality of pins 112.As a result, when the leaves 107 are attached to the collet trunk 110 bythe garter spring 111, the leaves 107 can flex inwardly and outwardlywith respect to the overall axis of the assembly 38. Each leaf 107further includes a gripping edge 113 that engages a cap on a vessel in amanner that is illustrated in FIG. 11. FIG. 9 also shows that theretaining screws 84 are received into the threaded bolts 114. In use,the threaded bolts 114 are received into the openings 119 in the collettrunk 110 and the screws 84 are received into the threaded bolts 114.The screws 84 can move parallel to the axis of the assembly 38 in thecollet adjustment slots 83 that are also illustrated in FIGS. 7 and 8.The two-part nature of the screws 84 and 114 permit the collet 86housing and the collet leaves 107 to be tightened in place in anappropriate relationship to a vessel as may be desired or necessary ingiven circumstances.

[0061] The present invention measures the pressure inside of a vessel bytransmitting the pressure through a needle that extends through a septumand into the vessel to the transducer 116 that converts the pressureinto an appropriate electrical signal for the processor or the display.FIG. 9 also illustrates these features in more detail as does FIG. 11.First, the needle 115 extends into the reaction vessel 105 (FIG. 11). Inturn, the needle 115 transmits the pressure, in the well-understoodfashion of fluid mechanics, to the transducer 116. In turn, thetransducer 116 transmits its signals through the wires 117. In a typicalarrangement (and although not specifically illustrated in FIG. 9), thetransducer 116 includes four wires: power and its ground, and signal andits ground.

[0062] The other elements in the left-hand portion of FIG. 9 helpmaintain the transducer 116 and the needle 115 in proper relationshipwith each other and with the vessel. Thus, FIG. 9 shows a needle holder120, which is fixed on the collet adjustment housing 86 using the screws121 which are respectively received in the screw holes 122 in thehousing 86. The transducer 116 is received in a transducer holder 123that also encloses a needle receptor 124 that receives the upper (cap)portion 125 of the needle 115. The transducer 116 includes a smallbushing 126 that receives the needle receptor 124, with the O-ring 127providing an additional pressure seal. The A clip ring 130 helps holdthese elements together in the transducer holder 123. FIG. 9 thusillustrates that when the collet assembly and transducer assembly areproperly assembled, the needle 115 passes axially through the needleholder 120, the housing 86, the collet trunk 110, and the vesselreceptor 106, and into the vessel itself, thus permitting the transducerto read the pressure in the vessel as desired.

[0063]FIG. 10 illustrates additional features of the instrument of thepresent invention in exploded fashion. A number of the elementsillustrated in FIG. 10 have already been described with respect to theother figures. These include the magnetron 46, the rectangular portion56 of the waveguide 55, the circular portion 57, the retaining rings 52and 53, and the interlock assembly 54. FIG. 10 illustrates theattenuator in a resting, but not fully engaged position with respect tothe retaining ring 52. A polymer bushing 51 is positioned between theretaining rings 52 and 53 and helps provide a better physical andmicrowave seal for the cavity 45.

[0064]FIG. 10 also illustrates a dielectric insert 95 that fits in thecavity 61 immediately adjacent the inner wall 62 of the cavity 61. Thedielectric insert 95 serves at least two purposes: first, the dielectricinsert 95 is preferably formed from a chemically inert material to helpprotect the interior of the cavity 61 from reagents. Preferred materialsinclude polymeric fluorinated hydrocarbons such aspolytetrafluoroethylene (PTFE).

[0065] Second, the insert 95 forms a portion of a preferred system forcooling the interior of the cavity 61 during or after chemical reactionshave been carried out therein and in response to the elevatedtemperatures generated by the reactions. In particular, in preferredembodiments, the waveguide 55 includes a gas inlet fitting (58 in FIGS.4 and 6) through which a cooling gas can be circulated into andthroughout the waveguide. In order to take advantage of this, the insert95 includes the circumferential channel 98 through which the cooling gascan flow. A series of small, radially-oriented openings (too small to beillustrated in the scale of FIG. 10) permit the gas to flow into thecenter of the cavity 61 and cool it and any vessels and reagents inside.Although the insert 95 changes the tuning characteristics of the cavity,the tuning can be adjusted as desired to compensate for the insert 95.Such tuning is familiar to those of ordinary skill in this art and canbe carried out without undue experimentation.

[0066]FIG. 10 also illustrates the stirring mechanics of the instrumentof the present invention. As illustrated therein, the stirrer motor 47is positioned on a motor platform leg 96 from which it drives a pulley97. In turn, the drive pulley 97 drives a belt 100 to thereby drive thedriven pulley 101. The driven pulley 101 contains one or two magnets102, which, because of their position on the driven pulley 101, orbitthe center of the bottom floor 64 of the cavity 61. When a magneticstirrer bar is placed in a vessel in the cavity 61 and the motor 47drives the pulleys 97 and 101, the motion of the magnets 102 will inturn drive the stirrer bar in the reaction vessel.

[0067]FIG. 10 also illustrates a liquid drain 103. The liquid (fluid)drain 103 works in conjunction with the floor openings 75 that are bestillustrated in FIG. 5 to allow any fluids that may collect in the cavity61 to drain through the openings 75 and then through the drain 103 to acollection point (not shown) which in a presently preferred embodimentcomprises a small removable trough located at the floor of theinstrument 20.

[0068]FIG. 10 further illustrates means for measuring the temperature ofitems (vessels and reagents) in the cavity, shown as the temperaturemeasuring device 104, which is positioned immediately below andcoaxially with the depending shaft 76 (FIG. 5) to thus have an opticallyclear view of the interior of the cavity 61. Accordingly, when thetemperature measuring device is an optical device, with an infraredsensor being preferred, it can accurately measure the temperature ofvessels or contents of vessels within the cavity and provide theappropriate feedback to the processor of the instrument. As known tothose familiar with such measurements, the infrared sensor 104 must beappropriately positioned and focused to record the proper temperature ofthe intended objects, but doing so is generally well understood by thoseof skill in this art and will not be otherwise described in detail.Indeed, particular and appropriate adjustments can be made on aninstrument-by-instrument basis without undue experimentation.

[0069] In preferred embodiments, the temperature measuring device 104 isan infrared sensor, of which appropriate types and sources are wellknown by those of skill in this art. Additionally, and although notillustrated in detail in FIG. 10, the driver pulley 101 also carries aninfra-red transparent window through which the sensor 104 can read theinfrared transmissions from the cavity 61. In preferred embodiments, thewindow is formed of an amorphous composition of germanium (Ge), arsenic(As) and selenium (Se), which provides the greatest accuracy, but at arelatively high cost. Thus, in other embodiments the window can beformed of infrared-transparent polymers such as polytetrafluoroethylene(PTFE) or polypropylene which provide accurate transmission at agenerally lower cost.

[0070] With respect to both pressure and temperature measurement, andthe processors referred to earlier, the instrument includes thecapability for moderating the application of microwave power in responseto the measured temperature or pressure. The method of moderating can beselected from among several methods or apparatus. A simplewell-understood technique is to carry out a simple “on-off” cycle orseries of cycles (i.e., a duty cycle). Another technique can incorporatea variable or “switching” power supply such as disclosed in commonlyassigned U.S. Pat. No. 6,084,226; or techniques and devices thatphysically adjust the transmission of microwaves, such as disclosed incommonly assigned U.S. Pat. Nos. 5,796,080 and 5,840,583.

[0071]FIG. 11 is a cross-sectional view of the relationship between theremovable attenuator 33, a reaction vessel 105, and the collet assembly91. In a broad sense, FIG. 11 illustrates the relationship between thepressure transducer 116, the needle 115, and the closure for the vessel,which is formed of the deformable metal portion 133 and the septum 134.The relationship is such that the collet assembly 91 urges thetransducer 116 and needle 115 towards the vessel 105 while concurrentlybearing against the septum 134 and while urging the vessel and collettowards one another to provide the appropriate pressure seal.

[0072] By urging the various elements together in such fashion, theinvention prevents the puncturable septum from becoming a weak point inthe pressure integrity of the vessel 105 and the transducer 116. As wellrecognized in this art, many chemical reactions will generate gases andin a closed system these generated gases will cause a correspondingincrease in gas pressure.

[0073] Many of the items illustrated in FIG. 11 are also illustrated inFIG. 9 and, thus, corresponding numerals will be used in each case. Inmore detail, the vessel 105 rests in the central opening 118 defined bythe removable attenuator 33. As illustrated in FIG. 11, the vessel 105includes an annular lip portion 109 that rests upon the inner opening118. In order to maintain the vessel in place while measuring thetemperature, the leaves 107 of the collet assembly are brought to bearagainst the removable attenuator 33 and, because of the threadedrelationships between the vessel receptor 106, the collet trunk 110, andthe collet housing 86, the collet can be brought to an appropriateposition and tightened there to maintain the leaves 107 in forcedcontact against the removable attenuator, while at the same time urgingthe vessel receptor 106 downwardly against the vessel 105. In turn, theposition of the collet trunk 110 with respect to the collet housing 86can be adjusted using the collet adjustment slot 83 and the threaded nutand bolt portions 84 and 114.

[0074] Accordingly, FIG. 11 shows that when the vessel is in place inthe removable attenuator 33, the collet assembly 91 can clamp it inplace and at the same time maintain an appropriate pressure against theseptum 134, while at the same time seating the needle 115 and its upperneedle portion (cap) against the transducer in a manner which permitsthe pressure to be accurately measured, while at the same timemaintaining the integrity of the vessel and preventing it from becomingdislodged when gases generated by the reaction increase the pressure inthe vessel 105.

[0075]FIG. 11 illustrates that the reaction vessel 105 includes aclosure shown as the cap assembly 132. The cap assembly 132 is, inpreferred embodiments, formed of a deformable metal ring 133 and apenetrable septum 134. The septum 134 is made of a material, preferablyan appropriate polymer or silicone related material, that can bepenetrated by the needle 115, but which will surround and seal againstthe needle 115 even after penetration, thus maintaining the pressureintegrity of the vessel 105. The ring 132 is formed of a metal thickenough to have appropriate pressure resistant properties, but which canbe deformed relatively easily, preferably with an ordinary clampingtool, to engage the lip portions 135 of the reaction vessel 105 andthereby seal the vessel. With the vessel so sealed by the cap assembly132, the leaves 107 of the collet assembly 91, are brought intoengagement with the attenuator 33 and the vessel 105, with the ledges orgripping edges 113 engaging the attenuator 33 in a horizontal fashionand the cap assembly 132 in a vertical fashion to help maintain thesealed integrity of the entire assembly when in use.

[0076] In this fashion, the needle 115 extends from the transducer,through the cap 132 and into the vessel 105 to provide pressurecommunication between the interior of the vessel 105 and the transducer116. The collet assembly 91 engages the transducer, the needle 115, thecap 132 and the vessel 105 in linear relationship so that the pressurein the vessel 105 is transmitted to the transducer 116 while the vesselis in use (i.e., a reaction taking place while microwaves are beingapplied).

[0077]FIGS. 12 and 13 illustrate some of the additional advantages ofthe removable attenuator system of the present invention. Many of theitems illustrated in FIGS. 12 and 13 have also been previously describedwith respect to the other Figures, and in such cases the same referencenumerals will again refer to the same items. Both FIG. 12 and FIG. 13are cross-sectional views with FIG. 12 being taken directly through thecenter of the cavity 45 and FIG. 13 being taken from a point at which anentire vessel is illustrated.

[0078]FIG. 12 shows the cavity housing 45, the inner cavity wall 62, thedielectric insert 95, and the removable attenuator 33. As illustrated inFIGS. 12 and 13, in the preferred embodiments of the invention theremovable attenuator 33, which comprises the second portion of the twoengaged portions that together form the upper horizontal wall of thecavity (the other being retaining ring 52), the attenuator 33 comprisesan outer cylindrical wall 39 and an inner cylindrical wall 49, the innerand outer walls being separated by and perpendicular to an annular floor48. The inner wall 49 thus provides a receptacle for receiving thevessel 105 therein, and likewise provides the attenuating functionrequired to prevent microwaves generated by the source and propagatedinto the cavity from propagating outside the cavity when the vessel 105is in place.

[0079]FIG. 13 is almost identical to FIG. 12 with the exception that thefirst attenuator 33 has been replaced a second attenuator 33′ and thevessel 105 has been replaced with the round bottom flask 105′illustrated in FIG. 13. It will be immediately seen that the removableattenuators 33 and 33′ provide a quick and easy method of exchangingreaction vessels without otherwise changing the size, capability,function or operation of the overall instrument 20. Thus, for a largervessel such as 105′ illustrated in FIG. 13, the outer wall 39 of theattenuator 33′ is essentially the same as the outer wall 39 of theattenuator 33 in FIG. 12. The inner cylindrical wall 49′, however, issomewhat taller (in the orientation of FIG. 13), defines a largerdiameter opening and provides for an attenuating function even thoughthe flask 105′ is larger than flask 105. By way of brief comparison,prior devices (e.g., U.S. Pat. No. 5,796,080) have attempted tocustomize the attenuator in a permanent sense for one particular sizedvessel. Accordingly, an instrument that was capable of handling asomewhat smaller vessel such as 105 illustrated in FIG. 12 could nothandle the larger vessel 105′ illustrated in FIG. 13. Furthermore,because the attenuator had to be sized to accommodate the largestpossible reaction vessels being used, the attenuator had to bepermanently large, rather than just large enough for the particularvessel being used.

[0080] As one further advantage of the removable attenuators 33 and 33′,in prior devices the diameter of the attenuator opening was kept largeenough to receive the largest portion of the vessel. With respect toFIG. 13, this required the opening to be large enough to receive thebulb portion of the round bottom flash 105′. In turn, a larger diameteropening requires a taller (longer) attenuator to prevent microwaves frompropagating beyond the attenuator.

[0081] In contrast, and as FIG. 13 illustrates, in the presentinvention, the attenuator need only be large enough to accommodate thenearby portions of the vessel 105′ rather than the largest portionsthereof. It will thus be understood as a further advantage that in somecircumstances (e.g., FIG. 12) the attenuator 33 is put in place first,after which the vessel 105 is placed in the attenuator 33 and the cavity61. In other circumstances (e.g., FIG. 13), the vessel 105′ is placed inthe cavity 61 first, after which the attenuator 33′ is put intoposition.

[0082] Accordingly, in another aspect the invention comprises a methodof carrying out chemical reactions using microwave assisted chemistry bycarrying out a first reaction in a first vessel of a particular size;removing the vessel and the attenuator 33 from the cavity; replacing thevessel with a new, differently sized vessel, and then replacing theattenuator with a new differently sized attenuator that neverthelessfits into the same opening.

[0083]FIGS. 14 and 15 illustrate some details of the reaction vessel105. FIG. 14 is a perspective view of the reaction vessel 105 alone, andillustrates that in certain (but not all) embodiments, it superficiallyrepresents a test tube in its cylindrical shape. As illustrated by thevessel 105′ in FIG. 13, the reaction vessel can be one of any number ofshapes and types while still incorporating the pressure-resistantaspects of the invention. FIG. 14 also illustrates the deformable metalportion 133 of the cap, along with an opening for the septum 134 (notshown) through which the needle 115 (not shown) can penetrate in amanner described with respect to the other drawings.

[0084] As stated previously, the vessel 105 is preferably pressureresistant; i.e., it can withstand pressures above atmospheric. Thiscapability enables reactions to be carried out at elevated pressures,which can offer certain advantages in some circumstances. For example,particular reaction mechanisms can change in a favorable manner atabove-ambient pressures, and in other circumstances, more efficient oreven different (and better) mechanisms will take place at above ambientpressures. Additionally, under most circumstances, an increased pressurewill produce or maintain an increased temperature, in accordance withthe ideal gas law and its several related expressions. In turn, highertemperatures generally favorably initiate or accelerate most chemicalreactions.

[0085]FIG. 15 illustrates some additional details of the vessel 105. Asshown therein, the vessel 105 has at least a cylindrical portion, and asillustrated in FIG. 15, may be entirely cylindrical, with thecylindrical portion being defined by the concentric inner and outerwalls 136 and 137 that terminate in a cylindrical opening 135. Asillustrated in FIG. 15, the cylinder includes an annular rim 140 thatextends outwardly from the circumference of the cylindrical opening 135and defines a rim circumference 141 that is concentric with thecylindrical portion of the vessel 105 and the cylindrical opening 135.

[0086] The vessel 105 further includes a curved outer wall portion 142between the concentric outer wall 137 and the rim circumference 141. Inthis regard, it has been discovered that under higher pressures, aperpendicular relationship between the outer wall 137 and the rim 140tends to be the weakest point under stress applied from the interior ofthe vessel 105. It has been discovered according to the presentinvention, however, that by providing the curved outer wall portion 142,the pressure resistance of the vessel can be significantly increased.Specifically, in current embodiments, a reaction vessel with a 90-degreerelationship at the portion described will withstand pressures up toabout 200 pounds per square inch (psi) before failing. The curved outerwall portion 142 of the present invention, however, can withstandpressures of up to about 1000 psi.

[0087] The invention has been described in detail, with reference tocertain preferred embodiments, in order to enable the reader to practicethe invention without undue experimentation. A person having ordinaryskill in the art will readily recognize that many of the components andparameters may be varied or modified to a certain extent withoutdeparting from the scope and spirit of the invention. Furthermore,titles, headings, or the like are provided to enhance the reader'scomprehension of this document and should not be read as limiting thescope of the present invention.

That which is claimed is:
 1. An instrument for microwave-assistedchemical processes that provides greater flexibility in carrying outmicrowave-assisted chemistry under varying conditions, said instrumentcomprising: a source of microwave radiation; a cavity in communicationwith said source; said cavity including at least one wall formed of twoengaged portions that form a barrier to the transmission of microwaveswhen so engaged; said engaged portions being disengagable from oneanother; and one of said portions further including amicrowave-attenuating opening.
 2. An instrument according to claim 1wherein said microwave attenuating portion supports a reaction vessel insaid cavity.
 3. An instrument according to claim 1 wherein said engagedportions form an upper horizontally-oriented wall of said cavity.
 4. Aninstrument according to claim 1 wherein one of said portions is fixed tothe remainder of said cavity and the other of said portions is removablefrom said fixed portion and thus from said cavity.
 5. An instrumentaccording to claim 4 wherein said removable portion includes saidmicrowave-attenuating opening.
 6. An instrument according to claim 5 andfurther comprising a second removable portion that is engageable withsaid fixed portion, and having a differently-sized microwave-attenuatingopening than said first removable portion for receiving differentlysized reaction vessels.
 7. An instrument according to claim 4 whereinsaid fixed engaged portion forms the perimeter of said upper wall andsaid removable engaged portion forms the remaining interior of saidupper wall.
 8. An instrument according to claim 7 wherein said portionwith said attenuating opening is circular and said perimeter forms acorresponding circular opening.
 9. An instrument according to claim 8further comprising means on said attenuator portion and said perimeterportion for engaging said portions by rotating said attenuator portionin said perimeter portion.
 10. An instrument according to claim 7 andfurther comprising a locking system on said perimeter portion for fixingsaid attenuator portion in place while said cavity is in use.
 11. Aninstrument according to claim 1 and further comprising means forpreventing microwaves from entering said cavity when said engagedportions are disengaged from one another.
 12. An instrument according toclaim 11 wherein said preventing means turn off said source when saidportions are disengaged from one another.
 13. An instrument formicrowave-assisted chemical processes that provides greater flexibilityin carrying out microwave-assisted chemistry under varying conditions,said instrument comprising: a source of microwave radiation; a cavity incommunication with said source; said cavity including an upperhorizontal wall formed of first and second engaged portions that form abarrier to the transmission of microwaves when so engaged; said firstportion defining a circular opening; and said second portion having acircular perimeter that corresponds in size to said circular opening;said first and second portions being disengagable from one another; andsaid second portion further including a microwave-attenuating opening.14. An instrument according to claim 13 wherein said microwaveattenuating second portion supports a reaction vessel in said cavity.15. An instrument according to claim 13 comprising means for engagingsaid first and second portions by placing said second portion into saidopening in said first portion, and then rotating said second portioninto its engaged position.
 16. An instrument according to claim 15 andfurther comprising means for preventing said source from generatingmicrowaves unless said second portion is in its rotated and engagedposition.
 17. An instrument according to claim 13 and further comprisingan additional second portion that is engageable with said first portion,and having a differently-sized microwave-attenuating opening than saidother first portion for receiving differently sized reaction vessels.18. An instrument according to claim 13 wherein said second portioncomprises: an outer cylindrical wall; an inner cylindrical wall; and anannular floor between and perpendicular to said inner and outercylindrical walls; said inner cylindrical wall having an axial dimensionsufficient to attenuate microwaves generated by said source andpropagated into said cavity.
 19. A method of increasing the efficiencyof microwave-assisted chemical reactions, the method comprising:carrying out a first chemical reaction in a reaction vessel in anattenuated cavity of a microwave instrument; removing the reactionvessel and the attenuator from the instrument; placing a differentreaction vessel and a differently-sized attenuator in the same cavity ofthe instrument; and carrying out a second chemical reaction in thedifferent vessel in the cavity of the instrument.
 20. A method accordingto claim 19 wherein the steps of carrying out the first and secondreactions comprises carrying out the same type of reaction.
 21. A methodaccording to claim 19 wherein the steps of carrying out the first andsecond reactions comprises carrying out different types of reaction. 22.A method according to claim 19 wherein the step of carrying out thesecond reaction comprises carrying our the second reaction in a reactionvessel that is larger than the reaction vessel used to carry out thefirst reaction.
 23. A method according to claim 19 wherein the step ofcarrying out the second reaction comprises carrying our the secondreaction in a reaction vessel that is smaller than the reaction vesselused to carry out the first reaction.
 24. A method according to claim 19wherein the step of placing the different vessel and differentattenuator comprises placing the attenuator in the instrument andthereafter placing the vessel in the attenuator.
 25. A method accordingto claim 24 comprising supporting the vessel in the cavity by supportingthe vessel in the attenuator.